1. Field of the Invention
The present invention concerns a microtome for producing thin sections, in which the cutting operation is performed by way of a relative movement between a cutting knife and an object. A drive system having a drive motor, a control circuit, and a handwheel is provided to generate the relative movement.
Microtomes are increasingly being automated in order to minimize the continuous stress on the operator and at the same time to ensure simplified handling. In addition, the throughput of specimens to be sectioned is increased with a correspondingly automated microtome. In automated microtomes, for example, developments have included not only automatically feeding the object onto the cutting knife, but additionally equipping the drive system with a motor that generates a relative movement between the object and the cutting knife. A microtome of this kind is depicted and described, for example, in WO 98 04 898 A1.
With automatically operating microtomes it has also been found, however, that in certain situations it is impossible to dispense with manual intervention by the operator. The motorized drive system must be operated as slowly as possible, for example, after an object has been changed in order to align the object, and when sectioning of the object first begins. With automated microtomes, however, only control panels with corresponding switches are provided to control operation. Sensitive, manually controlled operation can be achieved only to a limited extent with switches.
During alignment of the object, it is also necessary for the object and the cutting knife to be fed toward one another, then a visual check is made, and then a slight reverse motion is performed. These degrees of freedom are necessary for alignment. Once achieved, the alignment is then checked visually by feeding again, and is again corrected if necessary. To ensure perfect cuts, this procedure must be performed with the greatest of care. With simple rocker switches, a motor-driven microtome cannot be controlled with sufficient accuracy for such a procedure.
The motorized drive systems also suffer from the disadvantage that, in zero-current standby mode, the drive system can be moved manually. This is dangerous, in particular when a knife or preparation is being changed, since the operator""s hand may slip against the components, and can be pulled against the knife edge by the moving drive.
2. Description of the Related Art
U.S. Pat. No. 5,671,648 discloses a microtome for producing thin sections for microscopy. This microtome has a stationary cutting knife and an object holder, arranged on a rotatably mounted disk, with the object that is to be sectioned. The height of the disk can be changed in order to feed the object onto the cutting knife. The feed device is equipped with a motor and a control circuit. A drive-train linkage with a handwheel is provided as the drive device for the rotatable disk. In addition, a drive motor that is connected to the drive train can be arranged in the microtome. This document does not stipulate whether the drive motor replaces the handwheel, or how the drive motor is activated.
DE 88 09 096 U1 discloses a microtome having retractable operating knobs that are connected to a drive train for manual adjustment of the parameters that can be selected on the microtome, for example, section thickness, knife angle, etc. The drive train in this case is connected to an electronic generator that converts the rotary motion at the operating knobs into corresponding electrical signals. The drive motors for setting the parameters are controlled by way of a control device. No motor drive for preparation sectioning is provided in this microtome; all that is depicted is a conventional drive-train drive system using a handwheel.
It is one object of the present invention to provide an improved microtome having a motorized drive system that is capable as well of sensitive, manually controlled operation, and that assures a high level of operating safety, even in standby mode.